Conventionally, an electronic control unit (ECU) may be disposed in an engine compartment of a vehicle. For example, the ECU disclosed in a patent document 1 (i.e., Japanese Patent No.: JP-A-2006-49616) has a heat sink sealed on one side of an insert-molded housing made of an insulating resin. The ECU also has a cover sealed on the other side of the insert-molded housing. Further, the insert-molded housing of such an ECU has a connector integrally formed thereon.
As shown in the patent document 1, when a resin-made housing is disposed at a position between the heat sink and the cover, the housing may hinder heat dissipation from the heat sink to the cover because thermal conductivity of the resin-made housing is low. Further, to prevent creep from occurring to the housing, a screw hole for accepting a screw may have an iron collar inserted therein, for example. By having the iron collar, both ends of the iron collar and the heat sink/cover may have metal-metal contact with each other. However, even with such a structure, due to the heat conductivity of iron being lower than that of aluminum and a small contact area size, the heat conductivity for dissipating heat from the heat sink to the other parts via the collar may still be low.